The studies described in this proposal will aldow evaluation 1) of factors controlling protein degradation in perfused heart muscle, 2) of factors altering the latency and osmotic sensitivity of lysosomal enzyme activities, and 3) of a model of protein degradation involving lysosomes. Preliminary data indicate that in perfused rat hearts, degradation of protein is inhibited during anoxia and ischemia, while the latency of the lysosomal enzymes B-acteylglucosaminidase and cathepsin D is decreased. Attempts will be made to modify or reverse changes in the rate of protein degradation by varying pH, coronary flow, and rates of ventricular pressure development and by providing amino acids, fatty acids, and insulin in the perfusate. Direct effects on the uptake, release, and degradation of denatured and native proteins by isolated lysosomes will be studied using organelles purified by centrifugal and electrophoretic methods. By these methods we hope to define the "energy-requirement" and other factors affecting protein degradation and to identify factors controlling latency of enzyme activity. This information will provide the basis for new approaches to prevention of irreversible damage in the ischemic heart and for restriction of infarct size.